JP4265875B2 - Manufacturing method of surface emitting semiconductor laser - Google Patents

Description

[0001]
BACKGROUND OF THE INVENTION
  The present invention obtains laser light from an active layer that generates light on a substrate crystal and light generated from the active layer.In order to sandwich the upper and lower sides of the active layerHas a resonator structure,The present invention relates to a method of manufacturing a surface emitting semiconductor laser that generates light perpendicular to the substrate crystal.
[0002]
[Prior art]
In recent years, rapid speeding up of information transmission is required. Therefore, development of optical communication having a transmission rate of 10 Gb / s or more has been performed. In general, an optical module incorporating a semiconductor laser, a light receiving element, a drive circuit thereof, and the like is used for optical communication.
[0003]
A system as shown in FIG. 9 is known as an optical communication system using the above optical module and having a transmission rate exceeding 10 Gb / s. The optical module 907 transmits signal light from the semiconductor laser 901 in accordance with an external circuit 908 that operates the optical module. The optical signal transmitted from the other optical module is received by the light receiving element 905 driven by the light receiving element driving circuit 906. All optical signals are transmitted at high speed through the optical fiber 909.
[0004]
As the semiconductor laser 901, an edge-emitting laser using a gallium indium phosphide (GaInPAs) based semiconductor material as an active layer is mainly used. In general, GaInPAs-based lasers have a drawback that the threshold current increases greatly when the element temperature rises. Therefore, a Peltier element 904 for temperature stabilization is incorporated, and an auto power control (APC) circuit that constantly measures the light output fluctuation from the semiconductor laser 901 with the light receiving element 903 for monitoring and feeds back to the laser drive circuit 902 is incorporated. There is a need.
[0005]
Therefore, the number of parts constituting the optical module 907 is large, the drive circuit is complicated and the size is large, and the cost of the optical module itself is inevitably increased.
[0006]
On the other hand, surface emitting lasers are attracting attention as light sources suitable for high-speed optical modules. A surface-emitting laser is an optical resonator composed of an active layer that generates light, a current confinement layer for injecting current into a very small area of the active layer, and a pair of reflecting mirrors arranged so as to sandwich the active layer vertically. Constructed with a vessel. The surface emitting laser has a cavity length of only a few μm, which is much shorter than the cavity length of the edge emitting laser (several hundred μm), and has a high active volume because the volume of the active region is small. In addition, the beam shape is almost circular and it can be easily coupled to optical fibers. No cleaving process is required, enabling device inspection on a wafer-by-wafer basis. Excellent features in cost reduction such as laser oscillation with low threshold current and low power consumption. Have
[0007]
As for the oscillation wavelength of the laser, in recent years, a 1.3 μm surface emitting laser made of a new semiconductor material that can be formed on a gallium arsenide (GaAs) substrate such as gallium indium nitrogen arsenide (GaInNAs) or gallium arsenide antimony (GaAsSb) has been developed. Oscillations have been reported one after another, and the expectation for practical use of a long-wavelength surface emitting laser suitable for a single mode fiber capable of long-distance and high-speed transmission has been greatly increased. In particular, when GaInNAs is used for the active layer, it is predicted that electrons can be confined in a deep potential well in the conduction band, and the stability of characteristics with respect to temperature can be greatly improved.
[0008]
Due to the above advantages, if a long-wavelength surface emitting laser is realized, it is expected that an optical module suitable for use in a LAN can be obtained with high performance and low cost.
[0009]
The length of the optical resonator of the surface emitting laser is extremely short, and it is necessary to set the reflectance of the upper and lower reflecting mirrors to an extremely high value (99.5% or more) in order to cause laser oscillation. As the reflecting mirror, a multilayer film reflecting mirror formed by alternately stacking two types of semiconductors having different refractive indexes at a quarter wavelength thickness (λ / 4n: λ is a wavelength, n is a refractive index of a semiconductor material) is mainly used. in use.
[0010]
In order to obtain a high reflectance with a small number of stacked layers, it is desirable that the difference in refractive index between the two semiconductor materials used in the multilayer mirror is as large as possible. In addition, when the material is a semiconductor crystal, it is preferable that the material is lattice-matched with the substrate material in order to suppress lattice-mismatched dislocations. Currently, GaAs / aluminum arsenic (AlAs) based semiconductor materials or silicon dioxide (SiO2)₂) / Titanium dioxide (TiO₂A multilayer film reflector made of a dielectric material such as) is mainly used. The current confinement layer is indispensable for lowering the threshold current of the device. The current confinement layer is disposed between the active layer and the electrode for injecting current, and the current injected into the active layer is described as a minute region (hereinafter referred to as an aperture). To play a limited role. In order to achieve a single transverse mode, the aperture diameter must be as small as 2-3 μm at an oscillation wavelength of 850 nm and 5-6 μm at 1300 nm. Specifically, the AlAs layer introduced into the device structure is selectively oxidized from the lateral direction to produce aluminum oxide (Al_xO_y) The current mainstream method is to narrow the current only by the minute AlAs region remaining in the center by changing to an insulating layer. There is also a method of confining current by embedding a semiconductor material having a large band gap or a material doped with a conductivity type opposite to that in the element into the element.
[0011]
On the other hand, in the realization of an optical module having high speed characteristics exceeding 10 Gb / s, a surface emitting laser used as a light source needs to achieve high speed characteristics exceeding 10 Gb / s. For this purpose, it is indispensable to reduce the resistance (R) and capacitance (C) of the surface emitting laser element. FIG. 5 shows the relationship between resistance and capacitance and modulation characteristics. Since the capacitance of the surface emitting laser element is several hundred fF as a general value, it is necessary to reduce the element resistance to at least 50Ω or less in order to achieve high-speed modulation exceeding 10 Gb / s.
[0012]
As described above, AlAs / GaAs-based semiconductor multilayer mirrors are mainly used for surface emitting lasers. In the conventional device, an electrode is disposed on the upper p-type AlAs / GaAs-based semiconductor multilayer mirror, and current is injected into the active layer through the semiconductor multilayer reflector. At that time, the energy difference in the valence band of the AlAs / GaAs semiconductor has a problem that a hole having a large effective mass becomes a large resistance component at the heterointerface and increases the device resistance. As countermeasures, attempts have been made to introduce an AlGaAs semiconductor layer with gradually changing composition into the AlAs / GaAs heterointerface and to reduce the resistance component at the heterointerface by p-type doping only on the AlAs side. I came. However, it is very difficult to achieve an element resistance of 50Ω or less in a small-diameter aperture element that realizes a single transverse mode.
[0013]
In addition, a surface emitting laser having a structure in which current is injected without going through a high-resistance upper semiconductor multilayer mirror has been studied. As an example, FIG. 6 shows a device structure diagram of a surface emitting laser described in Japanese Patent Application Laid-Open No. 11-204875 developed by the present inventors. Here, 601 is an n electrode, 602 is an n-GaAs substrate, 603 is a lower multilayer reflector, 604 is a first GaAs spacer layer, 605 is a non-doped GaInNAs active layer, 606 is a second GaAs spacer layer, and 607 is a current constriction. 608 is a p-current introduction layer, 609 is a third p-GaAs spacer layer, 610 is a p-electrode, and 611 is an upper multilayer reflector.
[0014]
The current injected from the p-electrode 610 is guided from the third spacer layer 609 through the current introduction layer 608 to the aperture defined by the current confinement layer 607 and introduced into the active layer 605. That is, since the upper multilayer film reflecting mirror 611 is not interposed, the element resistance is reduced. Furthermore, in this structure, p = 1x10²⁰ cm^-3 By introducing a current introduction layer 608 having a doping concentration increased to an extent, the resistance component between the electrode and the aperture is reduced. Therefore, in this structure, an element resistance of 50Ω or less can be achieved in a small-diameter aperture element that realizes a single transverse mode.
[0015]
[Problems to be solved by the invention]
However, when the surface emitting laser shown in FIG. 6 was actually manufactured in a large number of lots, an element having a resistance value of about 20Ω and very good characteristics could be obtained, but there was a problem that the reproducibility of characteristics between lots was poor. . In particular, the resistance value was abnormally large and the electrical characteristics were poor. When the inventors of the present application have pursued the cause, it has been found that there is a problem in the joint surface between the third GaAs spacer layer 609 and the second GaAs spacer layer 606 which are part of the aperture. The bonding surface is a regrowth interface formed by re-growing the third spacer layer 609 after selectively removing the current confinement layer 607 and the current introduction layer 608, and due to a defect in the regrowth process. Characteristics deteriorate.
[0016]
Specifically, there are cases where the reproducibility of the minute etching performed before regrowth is poor and the crystallinity of the interface is not sufficient. On the other hand, if a small amount of etching process is omitted, Si is attached to the interface for some reason in the process of selectively removing the current confinement layer 607 and the current introduction layer 608, and the interface becomes an n-type conductivity type and then p. Even if the third spacer layer 609 of the mold is regrown, a pn junction and a depletion layer due to the pn junction are formed, which becomes a large resistance component.
[0017]
A first object of the present invention is to realize a semiconductor laser in which the influence of impurities generated at the regrowth interface of a semiconductor element having a regrowth interface between electrodes is reduced.
[0018]
A second object of the present invention is to reduce the resistance between electrodes in a surface emitting laser having a regrowth interface between the electrodes, and at the same time, a high-speed and high-performance surface emitting semiconductor laser with uniform characteristics when producing multiple lots and its surface emitting An object is to provide an optical module and an optical communication system that use a semiconductor laser, have a simple configuration, and are economical (low cost).
[0019]
[Means for Solving the Problems]
  In order to achieve the above object, the present inventionSurface emissionA semiconductor laser has a plurality of semiconductor layers formed by a regrowth process between electrodes.Surface emissionSemiconductorBodyIn the laser, the regrowth interface or its nearest surface is formed of a thin film having a high concentration of dopant. More specific of the present inventionThe manufacturing method of the surface emitting semiconductor laser is as follows.
  That isThe laser light is obtained from the active layer that generates light on the substrate crystal and the light generated from the active layer.In order to sandwich the upper and lower sides of the active layerResonator structureA surface emission that generates light perpendicular to the substrate crystalSemiconductor laserManufacturing methodBecauseA first step of forming a first spacer layer on the active layer, and selectively forming a current confinement layer and a current introduction layer on the first spacer layer by etching; and After the step, a second step of performing delta doping on the light transmission aperture portion on the first spacer layer and forming a second spacer layer on the delta-doped first spacer layer are performed. A surface-emitting semiconductor laser having the light-transmitting aperture portion surface as a regrowth interface, the regrowth interface being formed at a position closer to 1/8 wavelength from the position of the node of the optical standing wave in the surface-emitting laser It is a manufacturing method.
  Furthermore, in the present invention, by forming the current introduction layer on the current confinement layer, a cavity is formed on the current confinement layer and between the current confinement layer and the current introduction layer. Is useful.
[0020]
As the dopant, one having a small diffusion constant is suitable, and carbon is most suitable. The delta doping to a position within 10 nm from the interface is substantially the same as the delta doping to the regrowth interface because carriers move to the interface by the tunnel effect. The layer thickness of delta doping is 10 nm or less in consideration of manufacturing errors.
[0021]
According to the present invention, in the semiconductor laser in which the regrowth interface or its immediate surface has a high concentration of dopant, the p-type dopant is delta-doped to compensate for the n-type dopant Si described in FIG. The resistance component of the pn junction and the depletion layer due to the pn junction can be eliminated. That is, the substance that adheres to the interface and is contaminated is Si, but when a substance that becomes a p-type dopant adheres, it can be compensated by delta-doping the n-type dopant. The regrowth process is also widely used in semiconductor elements other than surface emitting lasers. Delta doping to the regrowth interface that electrically compensates for contaminant deposits is effective to improve the interface and device characteristics.
[0022]
Further, in a preferred embodiment of the surface emitting semiconductor laser of the present invention, in the surface emitting semiconductor laser, the regrowth interface is near the node position of the optical standing wave (preferably closer than 1/8 wavelength from the node position). Position).
[0023]
The positions of the antinodes and nodes of the optical standing wave are uniformly determined by the distance from the reflecting mirror and the oscillation wavelength considering the refractive index of the substance in the resonator. The distance between the resonators is exactly an integral multiple of the ½ wavelength thickness, and an antinode exists for each ½ wavelength thickness. In general, the active layer is placed at the antinode position of the optical standing wave in order to obtain the maximum gain (however, the position of the active layer does not determine the antinode position of the standing wave). In that case, the node of the optical standing wave exists at a position of 1/4, 3/4, 5/4 wavelength thickness from the active layer. As shown in FIG. 7, when the position of the regrowth interface is formed at the node of the optical standing wave, light does not exist at the node position, so the regrowth interface does not cause absorption and scattering. We also estimated how the light loss is affected by the position of the interface. FIG. 8 shows a simulation result of the reflection spectrum of an AlAs / GaAs multilayer mirror (25 periods) having one C-delta doped interface that becomes a light absorber. The difference between 100% and reflectivity indicates light loss. When the interface is located at a node, the loss is 0.04%, which is exactly the same as when no C-delta doped interface exists.
[0024]
On the other hand, when the interface was located in the belly, the loss was 0.17%, more than 4 times. In general, in a surface emitting laser having a high light density, an increase in loss greatly affects the optical characteristics of the element. Therefore, a four-fold increase in loss may not only reduce the efficiency to ¼, but also prevent the oscillation operation itself. In the above simulation, the C delta doped interface is treated as a light loss factor of the interface for easy quantification, but the same is true for the regrowth interface. Even if the interface is not exactly at the position of the node, it has an effect of improving the characteristics of the surface emitting semiconductor laser when it is closer than ± 1/8 wavelength thickness from the node.
[0025]
  A thin film with the dopant orThe regrowth interface is an optical standing waveWhen it is formed in the vicinity of the position of the node, it has the effect of simultaneously improving the static characteristics and the luminance characteristics of the semiconductor laser.
[0026]
DETAILED DESCRIPTION OF THE INVENTION
Although the surface emitting lasers of the examples described below have a p-junction interface, the means for eliminating the optical loss due to the regrowth interface by adjusting the position of the regrowth interface to the node of the optical standing wave is the interface. It does not depend on the conduction type.
<Example 1>
FIG. 1 is a sectional view showing the structure of an embodiment of a surface emitting laser according to the present invention.
In order to obtain laser light from the light generated from the active layer 104 and the active layer 104 that generate light on the substrate crystal 101, the active layer has a resonator structure in which the upper and lower sides of the active layer 104 are sandwiched between the reflecting mirrors 102 and 110, and is active. A second spacer layer 105 between the layer 104 and one of the reflectors 110, and a third spacer layer 109 semiconductor layer formed on the spacer layer 105 by a regrowth process, perpendicular to the substrate crystal; This is a surface emitting laser that emits light.
[0027]
The regrowth interface 108 is formed at a position closer than 1/8 wavelength from the position of the node of the optical standing wave. The emission wavelength of this example is 1.3 μm. A specific configuration and manufacturing method will be described below.
[0028]
In FIG. 1, 101 is an n-type GaAs substrate (n = 1x10).¹⁸ cm^-3, D = 300μm), 102 is an n-type GaAs / AlAs semiconductor multilayer reflector (n = 1x10)¹⁸ cm^-3), 103 is an n-doped first GaAs spacer layer (n = 1x10¹⁸ cm^-3, D = 1/2 wavelength thickness), 104 is a non-doped GaInNAs / GaAs strained quantum well active layer, 105 is a p-doped second GaAs spacer layer (p = 1 × 10¹⁷ cm^-3, D = 1/4 wavelength thickness), 106 is an n-type Ga (0.5) In (0.5) P current confinement layer (n = 1x10) lattice-matched with the GaAs substrate¹⁸ cm^-3, D = 50 nm), 107 is a p-type GaAs current introduction layer (p = 1x10²⁰ cm^-3, D = 1/2 wavelength thickness), 108 is the regrown interface, 109 is the p-type third GaAs spacer layer (p = 1x10)¹⁸ cm^-3, D = 3/4 wavelength thickness), 110 is a non-doped GaAs / AlInP semiconductor multilayer mirror, 111 is a p-side electrode, and 112 is an n-side electrode.
[0029]
In the lower semiconductor multilayer mirror 102, a high refractive index GaAs layer of 1/4 wavelength thickness and a low refractive index AlAs layer of 1/4 wavelength thickness were alternately laminated. In order to achieve a reflectance of 99.5% or higher, the number of mirror layers was set to 25 pairs. As the active layer 104, a strained quantum well layer having an effective band gap of 0.95 eV (wavelength: 1.3 μm) in which one 7 nm thick GaInNAs well layer is sandwiched between 10 nm thick GaAs barrier layers was used. For the thickness of the first spacer layer 103 and the second spacer layer 105, exactly half of the thickness of the active layer 104 was subtracted. As a result, the resonator length was accurately 1.5 wavelengths thick.
[0030]
The semiconductor layers 102-107 are formed by using a gas source molecular beam epitaxy apparatus.^-7Crystals were grown continuously in a high vacuum of Torr. Metals such as aluminum, gallium and indium were used for Group III materials, and metal arsenic, phosphine and nitrogen excited by plasma were used for Group V materials. Si and CBr4 were used as dopant materials. As shown in FIG. 1, a p-type GaAs current introduction layer 107 and a current confinement layer 106 are selectively etched sequentially with a sulfuric acid-based etching solution and a hydrochloric acid-based etching solution to form an aperture having a diameter of 5 μm. did. Return the wafer to the crystal growth system and irradiate the CBr4 beam with arsenic to p = 1x10 at the regrowth interface.¹² cm^-2 C delta dope was applied at a density of
[0031]
Thereafter, the third GaAs spacer layer 109 was regrown. The regrowth interface is at the node of the optical standing wave because it is 3/4 wavelength thick from the lower surface of the upper reflector. In addition, when selectively etching the current confinement layer 106, the cavity 113 was formed by controlling the etching time. During the regrowth, the p-type GaAs current introduction layer 107 above the cavity 113 is deformed, and the cavity 113 becomes tapered. Therefore, the optical loss at the portion where the aperture and the cavity 113 are in contact with each other is reduced, and the optical characteristics of the device are improved. Since the GaAs inside the aperture and the vacuum in the outer cavity have a large refractive index difference, a single transverse mode oscillation can be easily obtained.
[0032]
Subsequently, the upper semiconductor multilayer reflector 110 was grown. The upper semiconductor multilayer mirror 110 is formed by alternately laminating a ¼ layer thick GaAs layer and a ¼ layer thick GaAs substrate by lattice matching with an Al (0.5) In (0.5) P layer. In order to achieve a reflectance of 99.5% or higher, the number of mirror layers was set to 25 pairs. Next, the outside of the upper multilayer reflector 110 was dry etched until it reached the second GaAs spacer layer 109. Thereafter, a ring-shaped p-side electrode 111 and an n-side electrode 112 having an inner diameter of 7 μm and an outer diameter of 15 μm were formed. Finally, the outside of the ring-shaped p-side electrode 111 was etched to separate the elements.
[0033]
When a current was injected into the surface emitting laser, laser oscillation occurred at a threshold current of 100 μA. The laser light was emitted from the dielectric multilayer film reflecting mirror side, and the oscillation wavelength was 1.3 μm at room temperature. This surface emitting laser had a long element lifetime of 100,000 hours or more. Also, the yield among multiple lots was as high as 70% or more. The above performance is very excellent as a long wavelength surface emitting laser. Even when a material such as GaAsSb is used for the active layer, a 1.3 μm band surface emitting laser element can be fabricated.
<Example 2>
FIG. 2 is a sectional view showing the structure of another embodiment of the surface emitting laser according to the present invention.
An active layer 204 for generating light on the substrate crystal 201, and a resonator structure in which the upper and lower sides of the active layer 204 are sandwiched between reflecting mirrors 202 and 210 in order to obtain laser light from the light generated from the active layer, and active A second spacer layer 205 between the layer 204 and one of the reflectors 210 and a third spacer layer 209 semiconductor layer formed on the spacer layer 205 by a regrowth process, perpendicular to the substrate crystal; This is a surface emitting laser that emits light.
[0034]
The regrowth interface 208 is formed at a position closer than 1/8 wavelength from the position of the node of the optical standing wave. The emission wavelength in this example is 0.98 μm. A specific configuration and manufacturing method will be described below. 201 is an n-type GaAs substrate (n = 1x10¹⁸ cm^-3, D = 100μm), 202 is an n-type GaAs / AlAs semiconductor multilayer reflector (n = 1x10)¹⁸ cm^-3), 203 is an n-doped first GaAs spacer layer (n = 1x10¹⁷ cm^-3, D = 1/2 wavelength thickness), 204 is a non-doped GaInAs / GaAs strained quantum well active layer, 205 is a p-doped second GaAs spacer layer (p = 1 × 10)¹⁷ cm^-3D = 3/4 wavelength thickness), 206 is AlInO obtained by selective oxidation of Al (0.5) In (0.5) P lattice-matched with the GaAs substrate._xCurrent confinement layer (d = 100 nm), 207 is p-type GaAs current introduction layer (p = 1x10)²⁰ cm^-3, D = 1/2 wavelength thickness), 208 is the regrown interface, 209 is the p-type third GaAs spacer layer (p = 1x10)¹⁸ cm^-3, D = 3/4 wavelength thickness), 210 is SiO₂/ TiO₂A dielectric multilayer mirror, 211 is a p-side electrode, and 212 is an n-side electrode. In the semiconductor multilayer mirror 202, a high refractive index GaAs layer having a quarter wavelength thickness in a semiconductor and a low refractive index AlAs layer having a quarter wavelength thickness in a semiconductor are alternately stacked. In order to obtain a reflectance of 99.5% or more, the number of reflecting mirror layers was set to 25 pairs. As the active layer 204, a strained quantum well layer having an effective band gap of 1.27 eV (wavelength: 0.98 μm) is used by separating three 7 nm-thick GaInAs well layers by a 10 nm-thick GaAs barrier layer. The thickness of the first spacer layer 203 and the second spacer layer 205 was accurately subtracted from half of the thickness of the active layer 204, respectively. As a result, the resonator length was exactly 2 wavelengths thick.
[0035]
The semiconductor layers 202 to 207 were continuously grown in a vacuum of 50 Torr using a metal organic vapor phase epitaxy apparatus. Metals trimethylaluminum, trimethylgallium and trimethylindium were used as Group III materials, and dimethylhydrazine, phosphine and arsine were used as Group V materials. Disilane and dimethylzinc were used as dopant materials. As shown in FIG. 2, the AlInP layer that becomes the p-type GaAs current introduction layer 207 and the current confinement layer 206 is sequentially and selectively etched with a sulfuric acid-based etching solution and a hydrochloric acid-based etching solution as shown in FIG. An aperture was formed.
[0036]
The wafer was returned to the epitaxy apparatus and the third GaAs spacer layer 209 was regrown. P = 1x10 at the first 10 nm in contact with the regrowth interface 208 of the third GaAs spacer layer 209²⁰ cm^-3The delta dope was effectively made by applying a high dope. Since the regrowth interface 208 is at a position of 3/4 wavelength thickness from the lower surface of the upper reflecting mirror, it is at the node of the optical standing wave.
[0037]
Next, the outside of the portion where the ring-shaped p-side electrode 211 is formed is etched partway through the first GaAs spacer layer 205 to perform element isolation. Thereafter, AlInP was selectively oxidized from the outer peripheral portion in high-temperature steam to produce an AlInOx current confinement layer 206. Since AlInP does not exist in the aperture part, the selective oxidation of AlInP stopped reliably in the aperture part, and the aperture diameter could be controlled with high accuracy.
[0038]
Next, a ring-shaped p-side electrode 211 having an inner diameter of 10 μm and an outer diameter of 15 μm was formed by a lift-off method. Thereafter, the dielectric multilayer film reflecting mirror 210 was formed by a sputtering method. Dielectric multilayer reflector 210 is a high refractive index TiO with a quarter wavelength thickness in the dielectric.₂Low refractive index SiO with 1/4 wavelength thickness in layers and dielectrics₂It was produced by alternately laminating layers. In order to make the reflectance 99% or more, the number of layers was 7 pairs. Thereafter, as shown in FIG. 1, the outer side of the dielectric multilayer film reflecting mirror 10 was etched by Cl-based reactive ion beam etching to expose the p-side electrode 11. Finally, the n-side electrode 12 was formed.
[0039]
  Next, a ring-shaped p-side electrode 211 having an inner diameter of 10 μm and an outer diameter of 15 μm was formed by a lift-off method. Thereafter, the dielectric multilayer film reflecting mirror 210 was formed by a sputtering method. Dielectric multilayer reflector 210 was fabricated by alternately stacking a quarter-wave thickness high refractive index TiO2 layer in the dielectric and a quarter-wave thickness low refractive index SiO2 layer in the dielectric. . In order to make the reflectance 99% or more, the number of layers was 7 pairs. Then figure2Dielectric multilayer reflector by Cl-based reactive ion beam etching210Etch the outside of the p-side electrode211Was exposed. Finally, n-side electrode212Formed.
[0040]
Since the surface emitting laser 301 according to the present invention has a low element resistance, the element itself generates little heat and the temperature fluctuation is small. In addition, the threshold current value of the surface emitting laser itself is small, so that the change in the threshold current value during use is very small. Thereby, the element can be driven with a small and simple circuit. Therefore, the Peltier element and the APC circuit that are necessary for the conventional high-speed optical module shown in FIG. 4 are not required. Thereby, the number of parts can be greatly reduced, and the size of the drive circuit can be reduced. Therefore, the size of the optical module itself can be reduced, and a significant cost reduction can be realized. In addition, a high yield during device fabrication is also effective for cost reduction. Furthermore, since the optical module has a low resistance of the surface emitting laser and a small amount of heat generated from the element itself, the active layer is less likely to be deteriorated. Characteristics can be provided. As described above, the above effect becomes more remarkable in a surface emitting laser using GaInNAs or the like as an active layer material having excellent temperature characteristics that can confine electrons in a deep potential well in the active layer, for example, GaInNAs. .
<Example 4>
FIG. 4 is a sectional view showing the structure of still another embodiment of the semiconductor laser according to the present invention. This semiconductor laser is a lateral-type distributed feedback laser. (A) is sectional drawing perpendicular | vertical to a light beam direction, (b) is sectional drawing of the optical axis direction of (a).
On the p-GaAs substrate 401, a p-AlGaAs cladding layer 402, a diffraction grating 403, a p-AlGaAs guide layer 404, a GaNASSb unstrained active layer 405, and an n-AlGaAs cladding layer 407 are sequentially stacked to form a mesa stripe. A p-AlGaAs buried layer 412, an n-AlGaAs buried layer 413, and a p-AlGaAs buried layer 414 are buried on the side surface of the mesa stripe. Further, an n-AlGaAs planarization layer 415, an n-GaAs gap layer 408, and an SiO 2 current confinement layer 406 are laminated on the cladding layer and the buried layer, and an n-electrode 411 is formed. A p-electrode 412 is formed on the lower side of the p-GaAs substrate. Although the above configuration is the same as that conventionally known, in this embodiment, a layer containing a dopant is formed by carbon delta doping performed immediately before the growth of the p-AlGaAs guide layer, which is a regrowth layer on the diffraction grating. The adverse effect due to the impurities generated when forming the diffraction grating is reduced, and the resistance between the electrodes 411 and 412 is reduced.
[0041]
【The invention's effect】
According to the present invention, in a semiconductor optical laser manufactured through a regrowth process, device resistance is sufficiently low and ultrahigh-speed operation is possible by performing delta doping that electrically compensates for contaminant deposits at the regrowth interface. A semiconductor laser can be manufactured with good reproducibility. Therefore, high performance and low cost of a high-speed optical module using a semiconductor laser as a light source can be achieved. Furthermore, when the semiconductor laser is a surface emitting laser, the position of the regrowth interface with the delta-doped dopant is aligned with the node of the optical standing wave so that the regrowth interface does not cause absorption or scattering of the laser light. In addition to high-speed operation, the light emission characteristics of the semiconductor laser can be improved.
[Brief description of the drawings]
FIG. 1 is a cross-sectional view of an embodiment of a surface emitting semiconductor laser device according to the present invention.
FIG. 2 is a cross-sectional view of another embodiment of a surface emitting semiconductor laser device according to the present invention.
FIG. 3 is a configuration diagram of an optical communication system using the semiconductor laser of the present invention.
FIG. 4 is a cross-sectional view of another embodiment of a surface emitting semiconductor laser device according to the present invention.
FIG. 5 is a graph showing the relationship between resistance and capacitance and modulation characteristics.
FIG. 6 is a cross-sectional view of a conventional surface emitting laser element.
FIG. 7 is a diagram for explaining that the regrowth interface does not cause laser light absorption or scattering by matching the position of the regrowth interface with the node of the optical standing wave.
FIG. 8 is a characteristic diagram illustrating the influence of light loss depending on the position of the interface.
FIG. 9 is a configuration diagram of an optical communication system using a conventional semiconductor laser.
[Explanation of symbols]
101-semiconductor substrate, 102-lower multilayer mirror, 103-first spacer layer,
104-active layer, 105-second spacer layer, 106-current confinement layer, 107-current introduction layer,
108-re-growth interface, 109-third spacer layer, 110-upper multilayer reflector,
111-p side electrode, 112-n side electrode, 113-cavity.

Claims (2)

An active layer that generates light on a substrate crystal and a resonator structure that sandwiches the upper and lower sides of the active layer in order to obtain laser light from the light generated from the active layer, and a surface that generates light perpendicular to the substrate crystal A method for manufacturing a light emitting semiconductor laser, comprising:
A first step of forming a first spacer layer on the active layer and selectively forming a current confinement layer and a current introduction layer on the first spacer layer by etching;
A second step intends row delta doped to the light transmitting aperture portion of the first spacer layer after said first step,
Forming a second spacer layer on the delta-doped first spacer layer;
The surface light emission characterized in that the surface of the light transmission aperture portion is used as a regrowth interface, and the regrowth interface is formed at a position closer to 1/8 wavelength from the position of the node of the optical standing wave in the surface emitting laser. Semiconductor laser manufacturing method.   The current introduction layer is formed on the current confinement layer, thereby forming a cavity on the current confinement layer and between the current confinement layer and the current introduction layer. 2. A method for producing a surface emitting semiconductor laser according to 1.

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